Days after saying that a cell phone in a pants pocket set a sleeping man ablaze, Vallejo fire investigators have ruled out the phone.

Investigators from Nokia, one of the world's largest cell phone manufacturers, flew out to Vallejo, inspected the phone in question made by their company and convinced investigators that the phone didn't spontaneously combust, as fire officials initially said.

What, exactly, caused the fire remains a mystery.

Authorities had said the bizarre fire had started in the pants pocket, and the only item they found there during an investigation was a cell phone.

"There were no matches. There were no lighters. He wasn't smoking. The only source was the phone that was in his pocket," Vallejo Fire Department inspector and spokesman Bill Tweedy had said Monday. "I know he didn't spontaneously combust."

But Tweedy said a visit Wednesday by Nokia's experts changed his conclusion.

Under Fire Department supervision, Nokia's engineers checked the phone's wiring, tested it for short circuits, inserted the existing battery and hit the power button, said Tweedy, who was present during the test.

The phone -- a Nokia 2125i -- turned on.

"The phone didn't short out," Tweedy said. "It didn't overheat. The phone still works even though it's burned ... if the phone had shorted out, it wouldn't have turned on."

Picaso had fallen asleep on a plastic lawn chair in his residential hotel room when he was awakened by flames that spread from his right front pants pocket upward. The fire engulfed more than half his body and left him with second-and third-degree burns.

Firefighters found Picaso on the floor of the bathroom, where he had dragged himself.

Tweedy and other inspectors are still convinced the ignition source came from the pocket. But they don't know what it was.

"Whatever was there, other than the cell phone, is no longer there," Tweedy said late Wednesday night. "It was obviously a very intense fire because, obviously, the guy had third-degree burns."

Picaso, who is heavily sedated, has been interviewed by investigators only once since the Saturday night blaze, "but he didn't really know what happened," said Tweedy. "... He might not ever remember what happened, but I do know something lit the pants on fire," Tweedy said. "It wasn't spontaneous combustion. We eliminated everything but an ordinary flame source -- a match, a lighter, any smoking materials."

Tweedy said the Fire Department called Nokia in because "they offered their electrical engineers to come in and do testing that we can't afford to do."

The investigation is now over, Tweedy said. The original source of the fire will probably remain a mystery.

"He could have been smoking a cigarette, the cigarette fell into his pocket, and it started on fire," said Tweedy. "We don't know that. We weren't there."